Because I'm too cheap to pay for checked bags (hey, Disney is expensive enough!), we carried on 10 (!) plus stuffed animals. Each of the kids (2,4,6) had a backpack (considered personal item) with their toys for the flight (stored under the seat) and a carry on suitcase with their clothes (stored overhead). They also each had a stuffed animal. Two of them put their "pets" in their backpacks, but DS4 carried his the whole time. Never had a problem (other than the time it takes us to get on and off the plane!).
As for coats, we're from Colorado, so we didn't think we'd need them (we were there last week). During the day, I was in short sleeves, but when it rained and got late, we were glad to have coats with us.